PROJECT SUMMARY/ABSTRACT Loss-of-function mutations in the transcription factor methyl-CpG-binding protein 2 (MeCP2) result in the X- linked neurodevelopmental disorder Rett syndrome (RTT). The growth in research surrounding this monogenic disorder has resulted in development of preclinical models that recapitulate phenotypes such as stereotypic behavior of repetitive hand wringing, breathing abnormalities and deficits in motor and cognition. However, effective therapeutic treatments remain lacking. This can be attributed to the complex functions and diverse targets of MeCP2. Therefore, this research proposal has been developed to explore two arms of the therapeutic discovery efforts: genetic and pharmacological interventions. The design of this proposal provides the opportunity for the applicant to develop a breadth of training in neurophysiology and neuropharmacology spanning molecular, electrophysiological and behavioral techniques. In recent years, normalizing MeCP2 expression using gene therapy has garnered significant attention as a one-size fits all intervention for RTT. However, difference in MECP2 pathological mutations between patients introduces subpopulations that could further complicate an already narrow therapeutic index. Specifically, we hypothesize that patients with hypomorphic mutations could be at a greater risk for adverse effects (AEs) that mimic phenotypes of a related disorder, MECP2 Duplication syndrome. Behavioral and electrophysiological presentations of these possible MeCP2-mediated AEs are proposed to be evaluated by generating mice that harbor both a specific hypomorphic mutation and express a wild-type MeCP2 allele. To complement the genetic approach and circumvent these possible MeCP2-mediated AEs, a downstream target of MeCP2, metabotropic glutamate receptor 3 (mGlu3), will be targeted pharmacologically. mGlu3 has been demonstrated to have a functional role in cognition, and its expression has been consistently shown to be decreased in mouse models of RTT. We have preliminary data that suggests mGlu3 plays a significant role in long-term synaptic plasticity; additionally, we have generated data showing that mGlu3 expression is clinically relevant, as mGlu3 mRNA expression is significantly decreased in brain autopsy samples from patients clinically diagnosed with RTT. Therefore, we hypothesize that decreased mGlu3 expression contributes to cognitive phenotypes in RTT and that pharmacologically potentiating mGlu3 function will improve these phenotypes in RTT model mice.